Lightning arrester with a rupturable diaphragm for gas pressure release

ABSTRACT

A voltage surge arrester comprises one or more columns of stacked spark gaps and resistors located within a closed casing and which are connected electrically in series. In order to prevent the casing from fracturing as a result of the high thermal and mechanical stresses which are created by arcing within the casing, the spark gaps and resistors are given an annular configuration thereby to establish a continuous and approximately central channel through them and a pressure relief device is situated in the immediate vicinity of each end of the channel.

United States LIGHTNING ARRESTER WITH A RUPTURABLE DIAPHRAGM FOR GAS PRESSURE RELEASE 5 Claims, 1 Drawing Fig.

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Field of Search References Cited UNITED STATES PATENTS 3,144.582 8/1964 Sorrow et al 315/36 3,144.583 8/1964 Sorrow et al..... 3l5/36 3,290,547 12/1966 Sankey 315/36 Primary ExaminerRoy Lake Assistant ExaminerC. R. Campbell Attorney-Pierce, Scheffler & Parker ABSTRACT: A voltage surge arrester comprises one or more columns of stacked spark gaps and resistors located within a closed casing and which are connected electrically in series. In order to prevent the casing from fracturing as a result of the high thermal and mechanical stresses which are created by arcing within the casing, the spark gaps and resistors are given an annular configuration thereby to establish a continuous and approximately central channel through them and a pressure relief device is situated in the immediate vicinity of each end of the channel.

LIGHTNING ARRESTER WITH A RUPTURABLE DIAPHRAGM FOR GAS PRESSURE RELEASE The invention relates to a voltage surge arrester of which the active part consists of at least one column of stacked spark gaps and resistors located in a closed casing which is provided at least at one point, with a pressure release device. the resistors being ring-shaped. When the active part of a surge ar rester is overloaded, the casing of the arrester is subjected to high thermal and mechanical stresses due to the are which occurs inside the arrester and this can cause the casing to explode.

It is known to provide a fracture safety device for instance in the form a diaphragm, which provides a passage to the atmosphere for the pressure wave and furthermore a separating layer of heat-insulating material in the form of a protective cylinder of organic or anorganic material arranged within the casing for the purpose of protecting the latter (Swiss Pat. No. 289,179). Despite the fracture safety device, a sudden short pressure stress occurs so that the insulator casing or the protective cylinder have to be amply dimensioned and this increases the cost of the arrester, especially in the case of arresters in the medium voltage range.

Furthermore it is known to cause the-arc to ignite by means of fuselike connecting leads located in a central pressure tight tube, in order to relieve the arrester elements (Swiss Pat. No. 391,859). The fusible conductors are arranged in series with the conductor elements. In order to prevent the active elements from being damaged, it is essential that the response limit of the fusible conductors be considerably below the thermal loading limit of the active elements of the arrester, with the result that the utilization factor of the arrester is poor.

In connection with a voltage surge arrester having voltagedependent resistors and spark gaps in parallel with some of the resistors, it is known to make the resistors ring shaped and to locate the parallel gaps within the annular resistors. The object of this arrangement is that when a voltage surge occurs the spark gaps come into operation one after the other, the values of resistors being graduated (German Pat. No. 596, 097). In this arrangement the annular resistors and the parallel spark gaps are located in a special cylindrical insulator, whilst the additional disc-shaped resistors together with their spacing elements are to be found in the actual casing of the arrester, so that no proper explosion protection is achieved.

The object of the present invention is to provide a simple and cheap solution for obtaining an explosion-proof surge arrestor, whereby it is possible without any special additional measures to control the thermal and mechanical stresses resulting from over-voltages. In accordance with the invention it is therefor proposed that the spark gaps, which also have an annular shape, and the resistors should be so arranged that the stacked column has a continuous approximately central channel, a pressure release device being provided in the immediate vicinity of each end of the channel.

The invention will now be explained more fully by means of a constructional example shown in the drawing.

The FIGURE shows a sectional view of a voltage surge arrester for a medium voltage located in an insulting casing l, for instance consisting of ceramic material, and provided at each end with a flange 2 which is cemented to the casing. Screwed on to each flange is a cover 3 with an intermediate seal 4 so that a closed casing is obtained. The covers 3 are not solid but have a central opening which is closed by a fracture diaphragm 5. A stack of resistors 6 and spark gaps 7 is located inside the insulating casing l. The resistors and spark gaps are of annular shape and are so assembled that they are in close contact and have a channel 8 which passes through the middle of the stack. Each end of the channel 8 is in communication with a chamber 9 which is in close proximity to a diaphragm 5. An important feature of this arrangement is that the channel 8 has practically no communication with the annular gap 10 between the insulator l and the stack, so that when disturbing arcs occur all internal pressure stresses are kept away from the insulator l. The axial surfaces of the resistors are metallized. When the axial surfaces are not completely plane, it IS expedient to insert soft metallic rings between the annular resistors 6 when they are being stacked, so that there is a tight joint between the adjoining resistors. Furthennore it is also expedient to provide the resistors 6 with a conical recess 6a at least on one side of each resistor, whereby the thickness of the resistors is smallest in the region of the central channel 8 so that any breakdown of the resistor elements due to thermal overloading will occur near the channel 8 and the resulting ionized gases will pass into the channel 8 and not into the annular gap 10. The spark gaps 7 are so constructed that between neighboring insulating discs 7a, there is always a sparking chamber 7b in which the electrodes 70 are located at each side of the central channel or bore. The insulating discs 7a have a labyrinth type of seal located at the edge 7d. The electrodes 70 of the spark gaps are connected from one stage to the next by conductor 7e, so that a multiple spark gap is obtained. The first and last electrode are joined by similar conductors 7e to metallic discs 7f which establish contact with the neighboring resistors 6. Due to the fact that the disturbing arcs and the accompanying pressure rises which occur when the arrester is overloaded are restricted to the channel 8 as a result of the construction according to the invention, and the overpressure is released by the fracture of the diaphragm 5 without the insulator housing 1 being stressed at all, it is possible to control overloads and subsequent thermal and mechanical stresses in an absolutely reliable manner.

The invention can also be applied to surge arresters which have several columnlike stacks of elements located in a common casing in a known manner. In this case each stack has a central channel which ends at the corresponding pressure release device. In certain cases it may be an advantage if the pressure release device may be in the form of a safety valve.

1 claim:

1. Voltage surge arrester the active part of which consists of at least one column of stacked spark gaps and resistors said arrester being located in a closed casing which is provided at least at one point with pressure release device, said resistors being ring shaped, characterized in that the spark gaps and the resistors are assembled in such a manner that the stack has a continuous approximately central channel and that a pressure release device is provided in the immediate vicinity of each end of said channel.

2. Arrester as in claim 1, characterized in that the thickness of the resistors is smallest in the region of the central channel and increases on all sides in the radially outward direction.

3. Arrester as in claims 1 and 2, characterized in that the end surfaces of the resistors are in mutual contact by way of intermediate metallic rings, said rings serving to maintain electrical contact and to form a tight joint between said resistors.

4. Arrester as in claim 1, characterized in that the pressure release device is in the form of a safety valve.

5. Arrester as in claim 1, characterized in that the pressure release device is in the form of a fracture diaphragm. 

1. Voltage surge arrester the active part of which consists of at least one column of stacked spark gaps and resistors said arrester being located in a closed casing which is provided at least at one point with pressure release device, said resistors being ring shaped, characterized in that the spark gaps and the resistors are assembled in such a manner that the stack has a continuous approximately central channel and that a pressure release device is provided in the immediate vicinity of each end of said channel.
 2. Arrester as in claim 1, characterized in that the thickness of the resistors is smallest in the region of the central channel and increases on all sides in the radially outward direction.
 3. Arrester as in claims 1 and 2, characterized in that the end surfaces of the resistors are in mutual contact by way of intermediate metallic rings, said rings serving to maintain electrical contact and to form a tight joint between said resistors.
 4. Arrester as in claim 1, characterized in that the pressure release device is in the form of a safety valve.
 5. Arrester as in claim 1, characterized in that the pressure release device is in the form of a fracture diaphragm. 